A wide range of techniques has been developed for extracting protected data from supposedly secure integrated circuits, such as processors used in smart cards. Some of these techniques are based on fault generation: intentionally subjecting the processor to abnormal environmental conditions in such a way as to cause malfunctions that provide access secret data. For example, “glitch attacks” deliberately generate a malfunction that causes one or more flipflops to adopt the wrong state, with the result that security measures in the processor software may be bypassed. Glitches that may be used for this purpose include clock frequency transients, power supply transients, and external electrical field transients. Other known types of environmental fault-based attacks involve application of light or heat.
In response to threats of this sort, some smart cards include detectors that sense potentially-threatening environmental changes, such as clock or power glitches. Upon detecting such a change, the detector typically invokes appropriate countermeasures, such as shutting down or otherwise altering operation of the processor to prevent access by the attacker to secret information.